Film having high breathability induced by low cross-directional stretch

ABSTRACT

A breathable, substantially liquid impermeable film and laminate are provided for use in a wide variety of personal care garments and protective garments. The film, and laminate containing the film, are extendible in a cross-direction to a stretched width which is at least 25% greater than an original, unstretched width. The film and laminate have a first water vapor transmission rate of at least about 500 grams/m 2 -24 hours coinciding with the unstretched width. The film and laminate have a much higher second water vapor transmission rate which is at least about 225% of the first water vapor transmission rate, and not less than about 4000 grams/m 2 -24 hours, coinciding with a stretched width that is only 25% greater than the stretched width.

This application is a divisional of U.S. application Ser. No.09/751,414, filed on Dec. 28, 2000 which claims benefit of 60/201,830filed May 3, 2000.

FIELD OF THE INVENTION

This invention is directed to breathable films and laminates containingthem. Most of the moisture vapor breathability is induced by stretchingthe films by a small amount in the cross direction.

BACKGROUND OF THE INVENTION

Laminates which are breathable to water vapor but substantiallyimpermeable to liquid water are known in the art, and are commonly usedin diaper backings, other personal care absorbent garments, medical andindustrial protective garments, and the like. These laminates may becomposed of a breathable, stretch-thinned filled film and a spunbondweb. The breathable film can be formed by blending one or morepolyolefins with an inorganic particulate filler, forming a film fromthe mixture, and stretching the film to cause void formation around thefiller particles. The resulting film may have thin polymer membranesaround the filler particles which permit molecular diffusion of watervapor, while the overall film substantially blocks transmission ofliquid water, or may have micropores going through the film. Thebreathable film can be laminated to a nonwoven web, for instance, aspunbond web, by thermal or adhesive bonding. The spunbond web addsabrasion resistance, strength and integrity to the breathable laminate,and provides a soft, cloth-like feel.

One trend affecting the personal care absorbent garment industry, andthe protective garment industry, involves the demand and need forproducts with higher breathability to water vapor, which retain orincrease the barrier to water, blood and other liquid substances. Thistrend reflects the demand for increased wearer comfort without loss ofbarrier performance. Another trend affecting these industries involvesthe demand and need for products having better fit, which conform to thecontours of the wearer's body.

Still another trend involves the demand and need for products which areless expensive to produce, and which use less materials withoutsacrificing desirable product characteristics. Still another trendinvolves the demand and need for laminates having higher breathabilityto moisture vapor in selected regions of the laminates. In diapers andother pant-like absorbent articles, liquid can accumulate in the crotchregion. When this happens, heat from the wearer's body can cause thespace between garment and the wearer to become saturated with watervapor, facilitating the occurrence of diaper rashes and other skinirritations. The best way to effectively vent the water vapor is throughother regions of the garment which are not affected by the pool ofliquid in the crotch.

SUMMARY OF THE INVENTION

The present invention is directed to a breathable film, and a breathablelaminate including the film and at least one nonwoven web. The film hasa first state in which it has not been extended in the cross-direction,and a second state in which it has been extended by 25% in thecross-direction. The film has a first water vapor transmission rate(WVTR) of at least 500 grams/m²-24 hours in the first state, and asecond WVTR in the second state, determined from the WVTR test proceduredescribed below. The second WVTR in the second state is at least about225% of the first WVTR, and is not less than about 4000 grams/m²-24hours. The large increase in WVTR between the first state and the secondstate occurs solely as a result of stretching the film by about 25% inthe cross-direction.

The present invention is also directed to a breathable laminate whichexhibits similar properties. The nonwoven web is selected, and is bondedto the breathable film, so as not to substantially impair thebreathability of the film. In essence, the breathability of the laminateis determined by the breathability of the film, although the WVTR valuesmay be somewhat lower for the laminate depending on the bondingtechnique employed. The laminate has a first state in which it has notbeen extended in the cross-direction, and a second state in which thelaminate (including the film) has been extended by about 25% in thecross-direction of the film. The laminate has a first WVTR in the firststate which is at least 500 grams/m²-24 hours, determined from the WVTRtest procedure described below. The laminate has a second WVTR in thesecond state which is at least 225% of the first WVTR, and is not lessthan about 4000 grams/m²-24 hours.

The breathable laminate can be used in a wide variety of personal careabsorbent articles and protective garments. In one embodiment, thelaminate is used as a backsheet in a disposable diaper or otherpant-like absorbent garment. The diaper or other pant-like garment isinitially undersized, representing a material savings. To don thegarment on a wearer, the front and back regions in the garment(including the laminate) are stretched by about 25% of the originalwidth of the laminate, in the cross-direction of the film. Thisstretching causes the front and back regions to have substantiallyhigher WVTR than the crotch region, which is not significantly stretchedduring donning.

With the foregoing in mind, it is a feature and advantage of theinvention to provide a breathable film, and a correspondingfilm/nonwoven web laminate, to which high moisture vapor breathabilitycan be induced by only minor stretching in the cross-direction of thefilm.

It is also a feature and advantage of the invention to provide agarment, such as a pant-like absorbent garment, to which selectedregions of high breathability can be induced by minor stretchingoccurring during donning of the garment.

The foregoing and other features and advantages of the invention willbecome further apparent from the following detailed description of thepresently preferred embodiments.

Definitions

The term “extendible” is used herein to mean a material which uponapplication of a stretching force, can be extended in a particulardirection (e.g., the cross-direction), to a stretched dimension (e.g.,width) which is at least 25% greater than an original, unstretcheddimension. When the stretching force is removed after a one-minuteholding period, the material preferably does not retract, or retracts bynot more than 30% of the difference between the stretched dimension andthe original dimension. Thus, a material having a width of one meter,which is extendible in the cross direction, can be stretched to a widthof at least 1.25 meters. When the stretching force is released, afterholding the extended width for one minute, a material stretched to awidth of 1.25 meters will preferably not retract, or will retract to awidth of not less than 1.175 meters. Extendible materials are differentfrom elastic materials, the latter tending to retract most of the way totheir original dimension when a stretching force is released. Thestretching force can be any force sufficient to extend the material tobetween 125% of its original dimension, and its maximum stretcheddimension in the selected direction (e.g., the cross direction) withoutrupturing it.

The “percent retraction” is determined when an extended material isrelaxed to where the retractive force drops below 10 grams for a 3-inchwide sample. “Percent permanent set” is 100 minus “percent retraction.”

The term “inelastic” refers both to materials that do not stretch by 25%or more and to materials that stretch by that amount but do not retractby more than 30%. Inelastic materials include extendible materials, asdefined above, as well as materials that do not extend, e.g., which tearwhen subjected to a stretching force.

The term “machine direction” as applied to a nonwoven web, refers to thedirection of travel of a conveyor passing beneath the spinnerette orsimilar extrusion or forming apparatus for the filaments, which causesthe filaments to have primary orientation in the same direction. Whilethe filaments may appear wavy, or even randomly oriented in a localizedsection of a nonwoven web, they usually have an overall machinedirection of orientation which was parallel to the movement of theconveyor that carried them away from the extrusion or forming apparatus.

The term “machine direction” as applied to a film, refers to thedirection on the film that was parallel to the direction of travel ofthe film as it left the extrusion or forming apparatus. If the filmpassed between nip rollers or chill rollers, for instance, the machinedirection is the direction on the film that was parallel to the surfacemovement of the rollers when in contact with the film.

The term “machine direction” as applied to a laminate including at leastone film and at least one nonwoven web, refers to the machine directionof the film component of the laminate.

The term “cross direction” for a nonwoven web, film, or laminate refersto the direction perpendicular to the machine direction. Dimensionsmeasured in the cross direction are referred to as “width” dimensions,while dimensions measured in the machine direction are referred to as“length” dimensions.

The terms “breathable film,” “breathable laminate” or “breathable outercover material” refer to a film, laminate, or outer cover materialhaving a water vapor transmission rate (“WVTR”) of at least about 500grams/m²-24 hours, using the WVTR Test Procedure described herein. Theterm “higher breathability” simply means that a second material has ahigher WVTR than a first material. Breathable materials typically relyon molecular diffusion of vapor, or vapor passage through micropores,and are substantially liquid impermeable.

The term “liquid water-permeable material” refers to a material presentin one or more layers, such as a nonwoven fabric, which is porous, andwhich is liquid water permeable due to the flow of water and otheraqueous liquids through the pores. The spaces between fibers orfilaments in a nonwoven web can be large enough and frequent enough topermit leakage and flow of liquid water through the material.

The term “nonwoven fabric or web” means a web having a structure ofindividual fibers or threads which are interlaid, but not in a regularor identifiable manner as in a knitted fabric. Nonwoven fabrics or webshave been formed from many processes such as, for example, meltblowingprocesses, spunbonding processes, air laying processes, coformingprocesses, and bonded carded web processes. The basis weight of nonwovenfabrics is usually expressed in ounces of material per square yard (osy)or grams per square meter (gsm) and the fiber diameters useful areusually expressed in microns. (Note that to convert from osy to gsm,multiply osy by 33.91.)

The term “microfibers” means small diameter fibers typically having anaverage fiber denier of about 0.005-10. Fiber denier is defined as gramsper 9000 meters of a fiber. For a fiber having circular cross-section,denier may be calculated as fiber diameter in microns squared,multiplied by the density in grams/cc, multiplied by 0.00707. For fibersmade of the same polymer, a lower denier indicates a finer fiber and ahigher denier indicates a thicker or heavier fiber. For example, thediameter of a polypropylene fiber given as 15 microns may be convertedto denier by squaring, multiplying the result by 0.89 g/cc andmultiplying by 0.00707. Thus, a 15 micron polypropylene fiber has adenier of about 1.42 calculated as (15²×0.89×0.00707=1.415). Outside theUnited States the unit of measurement is more commonly the “tex,” whichis defined as the grams per kilometer of fiber. Tex may be calculated asdenier/9.

The term “spunbonded fibers” refers to small diameter fibers which areformed by extruding molten thermoplastic material as filaments from aplurality of fine capillaries of a spinnerette having a circular orother configuration, with the diameter of the extruded filaments thenbeing rapidly reduced as by, for example, in U.S. Pat. No. 4,340,563 toAppel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat.No. 3,802,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394to Kinney, U.S. Pat. No. 3,502,763 to Hartmann, U.S. Pat. No. 3,502,538to Petersen, and U.S. Pat. No. 3,542,615 to Dobo et al., each of whichis incorporated herein in its entirety by reference. Spunbond fibers arequenched and generally not tacky when they are deposited onto acollecting surface. Spunbond fibers are generally continuous and oftenhave average deniers larger than about 0.3, more particularly, betweenabout 0.6 and 10.

The term “meltblown fibers” means fibers formed by extruding a moltenthermoplastic material through a plurality of fine, usually circular,die capillaries as molten threads or filaments into converging highvelocity heated gas (e.g., air) streams which attenuate the filaments ofmolten thermoplastic material to reduce their diameter, which may be tomicrofiber diameter. Thereafter, the meltblown fibers are carried by thehigh velocity gas stream and are deposited on a collecting surface toform a web of randomly dispersed meltblown fibers. Such a process isdisclosed for example, in U.S. Pat. No. 3,849,241 to Butin et al.Meltblown fibers are microfibers which may be continuous ordiscontinuous, are generally smaller than about 1.0 denier, and aregenerally self bonding when deposited onto a collecting surface.

The term “film” refers to a thermoplastic film made using a filmextrusion process, such as a cast film or blown film extrusion process.This term includes films rendered microporous by mixing polymer withfiller, forming a film from the mixture, and stretching the film.

The term “microporous” refers to films having voids separated by thinpolymer membranes and films having micropores passing through the films.The voids or micropores can be formed when a mixture of polymer andfiller is extruded into a film and the film is stretched, preferablyuniaxially in the machine direction. Microporous films tend to havewater vapor transmission due to molecular diffusion of water vaporthrough the membranes or micropores, but substantially block the passageof aqueous liquids.

The term “polymer” includes, but is not limited to, homopolymers,copolymers, such as for example, block, graft, random and alternatingcopolymers, terpolymers, etc. and blends and modifications thereof.Furthermore, unless otherwise specifically limited, the term “polymer”shall include all possible geometrical configurations of the material.These configurations include, but are not limited to isotactic,syndiotactic and atactic symmetries.

The term “garment” includes pant-like absorbent garments and medical andindustrial protective garments. The term “pant-like absorbent garment”includes without limitation diapers, training pants, swim wear,absorbent underpants, baby wipes, adult incontinence products, andfeminine hygiene products.

The term “medical protective garment” includes without limitationsurgical garments, gowns, aprons, face masks, and drapes. The term“industrial protective garment” includes without limitation protectiveuniforms and workwear.

The term “neck” or “neck stretch” interchangeably means that the fabric,nonwoven web or laminate is drawn such that it is extended underconditions reducing its width or its transverse dimension by stretchinglengthwise or increasing the length of the fabric. The controlleddrawing may take place under cool temperatures, room temperature orgreater temperatures and is limited to an increase in overall dimensionin the direction being drawn up to the elongation required to break thefabric, nonwoven web or laminate, which in most cases is about 1.2 to1.6 times. When relaxed, the fabric, nonwoven web or laminate does notreturn totally to its original dimensions. The necking process typicallyinvolves unwinding a sheet from a supply roll and passing it through abrake nip roll assembly driven at a given linear speed. A take-up rollor nip, operating at a linear speed higher than the brake nip roll,draws the fabric and generates the tension needed to elongate and neckthe fabric. U.S. Pat. No. 4,965,122 issued to Morman, and commonlyassigned to the assignee of the present invention, discloses areversibly necked nonwoven material which may be formed by necking thematerial, then heating the necked material, followed by cooling and isincorporated herein by reference in its entirety. The heating of thenecked material causes additional crystallization of the polymer givingit a partial heat set. If the necked material is a spunbond web, some ofthe fibers in the web may become crimped during the necking process, asexplained in U.S. Pat. No. 4,965,122.

The term “neckable material” or “neckable layer” means any material orlayer which can be necked such as a nonwoven, woven, or knittedmaterial, or a laminate containing one of them. As used herein, the term“necked material” refers to any material which has been drawn in atleast one dimension, (e.g. lengthwise), reducing the transversedimension, (e.g. width), such that when the drawing force is removed,the material can be pulled back to its original width. The neckedmaterial generally has a higher basis weight per unit area than theun-necked material. When the necked material is pulled back to itsoriginal width, it should have about the same basis weight as theun-necked material. This differs from stretching/orienting the filmlayer, during which the film is thinned and the basis weight is reduced.Preferred nonwoven webs for use in the invention are made from aninelastic polymer.

The term “percent neckdown” refers to the ratio determined by measuringthe difference between the un-necked dimension and the necked dimensionof the neckable material and then dividing that difference by theun-necked dimension of the neckable material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a top plan view of a microporous film of the inventionwhich has not yet been stretched in the cross-direction.

FIG. 1(b) illustrates the film of FIG. 1(a), stretched in thecross-direction at both end regions, but not in the middle, to impacthigh breathability at both end regions.

FIG. 2 is a sectional view of a microporous film, taken along line 3—3in FIG. 1.

FIG. 3 illustrates a top view of a fibrous nonwoven web, which can be aspunbond web, which has not been necked.

FIG. 4 illustrates a top view of a fibrous nonwoven web, which can be aspunbond web, which has been necked.

FIG. 5 schematically illustrates a process that can be used to form thebreathable laminates of the invention.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIGS. 1(a), 1(b) and 2 illustrate a film 100 of the invention. Referringto FIG. 1(a), film 100 has a machine direction 102 and a cross-direction104, and has a first end region 106, a central region 108, and a secondend region 110. Film 100 as shown in FIG. 1(a) has not yet beenstretched in the cross-direction 104. In this first state, film 100 mayhave a first WVTR of at least about 500 grams m²-24 hours, suitably atleast about 1000 grams/m²-24 hours, desirably at least about 1500grams/m²-24 hours.

FIG. 1(b) illustrates the film 100 after both end regions 106 and 110have been stretched in the cross-direction 104, suitably to about 125%of their original width. The configuration of film 100 shown in FIG.1(b) corresponds to the type of stretching that would occur when film100 is used in a backsheet of a diaper or other pant-like absorbentgarment. The first and second end regions 106 and/or 110, whichcorrespond to the front and/or back of the garment, would experienceabout a 25% cross-directional stretch (to about 125% of their initialwidth) during donning of the garment on a wearer. The central region108, which corresponds to the crotch region of the garment, would notstretch in the cross-direction during donning. In accordance with theinvention, the first and/or second end regions 106 and 110 (in thesecond state, after 25% cross-directional stretching) may have a secondWVTR which is at least 225% of the first WVTR, suitably at least 250% ofthe first WVTR, desirably at least 300% of the first WVTR, with thesecond WVTR not being less than about 4000 grams/m²-24 hours. Suitably,the second WVTR may be at least about 5500 grams/m²-24 hours, desirablyat least about 7000 grams/m²-24 hours. The central region 106, whichremains in the first state (unstretched in the cross-direction) retainsthe lower WVTR values indicated for the film of FIG. 1(a). In essence,the 25% cross-directional stretch causes a large increase in WVTR, inthe selected regions.

The film of the invention is thus characterized both in terms of anorder of magnitude increase in WVTR resulting from a 25%cross-directional stretch, and a relatively high WVTR following the 25%cross-directional stretch. If the film 100 (or portion thereof) has arelatively high first WVTR of, say, 2000 grams/m²-24 hours before thecross-directional stretch, then the second WVTR of the stretched film(or stretched portion) is at least 225% of the first WVTR. However, ifthe film 100 has a relatively low first WVTR of, say, 500-1000grams/m²-24 hours, then the second, post-stretching WVTR is at least4000 grams/m²-24 hours and a higher order-of-magnitude increase isrequired.

After the cross-directional stretching, the highly breathable endregions of film 100 (as well as the central region) should remainsubstantially impermeable to liquid water. In order to achieve the highbreathability resulting from low cross-directional stretching, whileretaining liquid barrier, the film composition must be properlyselected. The microporous film 100, which may be a single-layer film ora multilayer film, has a primary breathable layer. In a firstembodiment, the primary breathable layer may be formed from acomposition including a single-site catalyzed olefin polymer, aZiegler-Natta catalyzed olefin polymer, and a particulate filler.Surprisingly, this composition has been found to yield a greater orderof magnitude increase in film WVTR resulting from 25% cross-directionalstretch than both a) an otherwise similar composition including thesingle-site catalyzed polymer and filler, without the Ziegler-Nattacatalyzed polymer, and b) an otherwise similar composition including theZiegler-Natta catalyzed polymer and filler, without the single-sitecatalyzed polymer. The film-forming composition should include about10-55% by volume particulate filler and about 45-90% by volume totalpolymer, suitably about 15-45% by volume particulate filler and about55-85% by volume total polymer, desirably about 25-40% by volumeparticulate filler and about 60-75% by volume total polymer. The term“volume” refers to the total volume occupied by the polymers and filler,and excludes air space. The large quantity of particulate filler, whichis preferably homogeneously disposed among the polymer, aids in theformation of voids when the film is stretched. The voids are separatedby thin polymer membranes which facilitate the transmission (i.e.diffusion) of water vapor while blocking the flow of liquid water.

The term “total polymer” includes both the single-site catalyzed olefinpolymer and the Ziegler-Natta catalyzed olefin polymer, as well as otheroptimal polymer ingredients which do not prevent the film from having afirst WVTR of at least 500 grams/m²-24 hours before cross-directionalstretching, and a second WVTR after 25% cross-directional stretchingwhich is a) at least 225% of the first WVTR, and b) not less than 4000grams/m²-24 hours. The total polymer may include about 10-90% by weightat the single-site catalyzed olefin polymer and about 10-90% by weightof the Ziegler-Natta catalyzed olefin polymer, suitably about 25-75% byweight of the single-site catalyzed olefin polymer and about 25-75% byweight of the Ziegler-Natta catalyzed olefin polymer, desirably about30-60% by weight of the single-site catalyzed olefin polymer and about40-70% by weight of the Ziegler-Natta catalyzed olefin polymer.

Suitable olefin polymers include polyolefins, such as polyethylene,polypropylene, polybutene and the like, as well as olefin copolymers.Suitable olefin copolymers include copolymers having a major weightfraction (e.g. 70-99% by weight) ethylene and a minor weight fraction(e.g. 1-30% by weight) of a C₃-C₁₂ alpha-olefin comonomer. Suchcopolymers are commonly known as linear low density polyethylenes (wherethe density is about 0.900-0.935 grams/cm³) or very low densitypolyethylenes (where the density is about 0.870 to less than 0.900grams/cm³). Suitable olefin copolymers also include copolymers having amajor weight fraction (e.g. 70-99% by weight) propylene and a minorweight fraction (e.g. 1-30% by weight) of a C₂ or C₄-C₁₂ alpha-olefincomonomer. The olefin polymer should be selected so that the film isextendible in the cross-direction, meaning that it can be stretched byat least 25% of its initial width without rupture or tear, and will notretract by more than 30% of the difference between the stretched widthand the initial width if the stretching force is removed.

Other examples of extendible olefin polymers include certain flexiblepolyolefins, for example propylene-based polymers having both atacticand isotactic propylene groups in the main polypropylene chain. Flexiblepolyolefins (FPO's) are sold by the Rexene Corporation. Also includedare heterophasic propylene-ethylene copolymers sold as “catalloys” bythe Himont Corporation. Heterophasic polymers are reactor blends formedby adding different levels of propylene and ethylene at different stagesin the reactor. Heterophasic polymers typically include about 10-90% byweight of a first polymer segment A, about 10-90% by weight of a secondpolymer segment B, and 0-20% by weight of a third polymer segment C.Polymer segment A is at least about 80% crystalline and includes about90-100% by weight propylene, as a homopolymer or random copolymer withup to 10% by weight ethylene. Polymer segment B is less than about 50%crystalline, and includes about 30-70% by weight propylene randomlycopolymerized with about 30-70% by weight ethylene. Optional polymersegment C contains about 80-100% by weight ethylene and 0-20% ofrandomly copolymerized propylene.

Olefin polymers made using single-site catalysts have a very narrowmolecular weight range. Polydispersity numbers (Mw/Mn) of below 4 andeven below 2 are possible for metallocene-produced polymers. Thesepolymers also have a controlled short chain branching distributioncompared to otherwise similar Ziegler-Natta produced type polymers. Itis also possible using a metallocene catalyst system to control theisotacticity of the polymer quite closely. In general, polyethylenepolymers and copolymers having a density of 0.900 grams/cc or greatertend to be less extendible, while those having a density below 0.900grams/cc are more extendible. In general, polypropylene polymers andcopolymers containing 0-10% of an ethylene or other alpha-olefincomonomer tend to be less extendible, while propylene-alpha olefincopolymers containing more than 10% comonomer are more extendible.

Commercial production of single-site catalyzed polymers is somewhatlimited but growing. Such polymers are available from Exxon-MobilChemical Company of Baytown, Tex. under the trade name ACHIEVE forpolypropylene based polymers and EXACT and EXCEED for polyethylene basedpolymers. Dow Chemical Company of Midland, Mich. has polymerscommercially available under the name AFFINITY. These materials arebelieved to be produced using non-stereo selective metallocenecatalysts. Exxon-Mobil generally refers to their catalyst technology assingle site or metallocene catalysts while Dow refers to theirs as“constrained geometry” catalysts under the name INSITE to distinguishthem from traditional Ziegler-Natta catalysts which have multiplereaction sites. Other manufacturers such as Fina Oil, BASF, Amoco,Hoechst and Mobil are active in this area and it is believed that theavailability of polymers produced according to this technology will growsubstantially in the next decade.

Without wishing to be bound by theory, it is believed that filmsproduced from single-site catalyzed olefin polymers and filler andstretched only in the machine direction to about 1.1-7.0 times theirinitial length, have relatively lower breathability due to the fact thatthe single-site catalyzed polymers are both tenacious and extendible,and do not readily form voids. Films produced from Ziegler-Nattacatalyzed olefin polymers and filler, and similarly stretched in themachine direction, form voids more readily and exhibit higherbreathability. The films of the invention, which contain both polymertypes in addition to the filler, somehow combine these properties byexhibiting relatively lower WVTR when stretched only in the machinedirection, yet much higher WVTR when further stretched only slightly inthe cross-direction.

FIG. 2 illustrates a cross-section of a breathable extendiblemicroporous film 100 that can be laminated to a nonwoven web to form abreathable laminate, as described below. The breathable microporous film100 can include a primary microporous core layer 112 formed from thecomposition described above. The breathable layer 112 may be combinedwith two thinner skin layers 122 and 124 which are used for bonding.Alternatively, the film 100 may include a primary microporous core layer112, and only one skin layer 122 or 124, or no skin layers.

The microporous layer 112 includes a polymer matrix 111, a plurality ofvoids 114 within the matrix surrounded by relatively thin microporousmembranes 113 defining tortuous paths, and one or more filler particles116 in each void 114. The layer 112 is microporous and breathable,wherein the microporous membranes 113 between the voids readily permitmolecular diffusion of water vapor from a first surface 118 to a secondsurface 120 of the film 100. Alternatively, some or all of themicropores can pass through the film, or can be interconnected toprovide through-passages. The polymer matrix 111 may include both thesingle-site catalyzed olefin polymer and the Ziegler-Natta catalyzedolefin polymer, as discussed above.

The filler particles 116 can include any suitable inorganic or organicfiller. The filler particles 116 are preferably small to producemicropores, in order to maintain liquid water barrier of the film 100.Generally, the filler particles should have a mean particle diameter ofabout 0.1-7.0 microns, preferably about 0.5-5.0 microns, most preferablyabout 0.8-2.0 microns. Suitable fillers include without limitationcalcium carbonate, non-swellable clays, silica, alumina, barium sulfate,sodium carbonate, talc, magnesium sulfate, titanium dioxide, zeolites,aluminum sulfate, diatomaceous earth, magnesium sulfate, magnesiumcarbonate, barium carbonate, kaolin, mica, carbon, calcium oxide,magnesium oxide, aluminum hydroxide and polymer particles. Calciumcarbonate is a presently preferred filler.

The filler particles 116 may be coated with a minor quantity (e.g. up to2% by weight) of a fatty acid or other material to ease their dispersionin the polymer matrix. Suitable fatty acids include without limitationstearic acid, or a larger chain fatty acid such as behenic acid.

The polymer composition, filler content, filler particle size and degreeof stretching are factors which help determine the breathability andliquid barrier of the extendible microporous film 100 in the laminate.Generally, the oriented microporous film 100 will be less than about 50microns thick, preferably less than about 30 microns thick, mostpreferably less than about 20 microns thick. The film 100 may beuniaxially stretched in the machine direction to about 1.1-7.0 times itsoriginal length to cause breathability, preferably to about 1.5-6.0times its original length, most preferably to about 2.5-5.0 times itsoriginal length prior to lamination to a nonwoven web. This machinedirection stretching, which is reflected in the first film state shownin FIG. 1(a), causes the film to have a low level of breathability,i.e., an WVTR of not more than about 1000 g/m²-24 hours. Stretchingtemperatures may range from about 38-150° C. depending on the specificpolymers employed, and are preferably about 70-95° C. The film 100 canbe prepared by cast or blown film coextrusion of the layers, byextrusion coating, or by any conventional layering process.

In the embodiment of FIG. 2, the microporous breathable film layer 112is adjacent one or two relatively thin outer skin layers 122 and 124, ina two or three-layer extendible film 100. The inclusion of one or twoskin layers improves film processability and can also contribute heatseal properties to the breathable extendible film 100. The polymers inthe outer layers 122 and 124 can be the same or different than thepolymers in the microporous layer 112. Preferably, the polymers in theouter layer or layers are extendible, have a lower softening point thanin the microporous layer 112, and contribute to the heat sealability ofthe film 100. To facilitate breathability, the skin layers 122 and 124may contain a particulate filler in any quantity up to the same amountas the microporous core layer 112, and the skin layers may bemicroporous as well after the film is machine direction orientated.

Also, the thickness and composition of the outer layers 122 and 124should be selected so as not to substantially impair the moisturetransmission through the breathable film 100. This way, the microporouscore layer 112 may determine the breathability of the entire film. Tothis end, the skin layer 122 and 124 is generally less than about 10microns thick, preferably less than about 5 microns thick. The combinedskin layers should constitute no more than 25% of the entire filmthickness, and preferably constitute about 2-15% of the film thickness,more preferably 3-5% of the total film thickness. Suitable extendibleskin layer polymers having low softening points include amorphousmetallocene or Ziegler Natta-catalyzed copolymers of ethylene with aC₃-C₂₀ alpha-olefin comonomer, having a density less than about 0.89grams/cc. Also suitable are amorphous poly alpha-olefin (APAO) polymerswhich can be random copolymers or terpolymers of ethylene, propylene,and butene, and other substantially amorphous or semi-crystallinepropylene-ethylene polymers. Also included are ethylene vinyl acetates,propylene vinyl acetates, ethylene methyl acrylates, and blends of anyof the foregoing polymers.

As explained above, one embodiment of the invention involves combining afirst polymer A which is a single-site catalyzed olefin polymer, with asecond polymer B which is a Ziegler-Natta catalyzed olefin polymer, anda filler, and using this composition to form the primary breathablemicroporous layer 112 of the film 100, or the only layer if film 100 ismonolayer. In a second embodiment, the first polymer A may be a higherdensity olefin polymer and the second polymer B may be a lower densityolefin polymer. The two polymers may be combined with a particulateinorganic filler and with each other in the same compositional rangesdescribed above. In particular, the first polymer A may be a very lowdensity polyethylene having a density of 0.870 to less than 0.900grams/cm³, and the second polymer B may be a linear low densitypolyethylene having a density of 0.900-0.935 grams/cm³.

The second embodiment of the film-forming composition may operate by asimilar principle as the first embodiment of the film-formingcomposition. The lower density olefin polymer is more readily extendibleand does not separate easily from the filler particles to form voids,when the film is stretched. The higher density olefin polymer is stifferand readily forms voids, yielding higher breathability, even when thefilm is only stretched in the machine direction. By combining the twopolymers and filler, a film is obtained which exhibits low WVTR whenstretched only in the machine direction, and much higher WVTR whensubsequently stretched by only 25% in the cross-direction.

In a third embodiment, the principles of the first and secondembodiments may be combined. The first polymer A may be a single-sitecatalyzed olefin polymer which also has a lower density, and the secondpolymer B may be a Ziegler-Natta catalyzed olefin polymer which also hasa higher density. For instance, the first polymer A may be a single-sitecatalyzed very low density polyethylene having a density of 0.870 toless than 0.900 grams/cm³. The second polymer B may be a Ziegler-Nattacatalyzed linear low density polyethylene having a density of 0.900 to0.935 grams/cm³. The two polymers may be combined with each other and aparticulate filler using the same compositional ranges described abovefor the first embodiment.

In a typical case, the film 100 will be oriented only in the machinedirection before being laminated to a nonwoven web, and will bestretched slightly in the cross-direction after lamination to yield agreatly improved WVTR. This means that the nonwoven web must also becapable of extending in the cross-direction, to accommodate thestretching of the film. Typically, the film and nonwoven web will bebonded together with the machine direction of the film substantiallyaligned with the machine direction of the nonwoven web. The bonding maybe accomplished using any technique which minimizes disruption of themoisture vapor transmission through the film. Suitable techniquesinclude thermal point bonding, ultrasonic point bonding, adhesivepattern bonding, adhesive spray bonding, and other techniques where thebonded areas cover preferably less than about 25% of the interfacebetween the film and nonwoven web.

A variety of nonwoven webs are suitable for use in the laminate of theinvention. Referring to FIG. 3, a nonwoven web 10, which can be aspunbond web, includes a plurality of individual thermoplastic fiberelements 12 intermittently bonded together using a bonding patternwhich, in this instance, includes a plurality of point bonds 14. Theindividual fibers 12 appear to have a wavy or somewhat randomorientation when viewed on a microscopic scale. When viewed on amacroscopic scale, so that the entire lengths of fibers 12 are visible,the fibers 12 have an overall primary direction of orientation which isparallel to a machine direction, represented by arrow 16. If thenonwoven web is spunbond, it may be intentionally produced with highmachine-direction filament orientation and thermal bonds orientedpredominantly in the machine direction. This will provide the spunbondweb with inherent cross-directional extendibility, much like thatexisting in a conventional bonded carded web.

The nonwoven web is preferably a spunbond web, but can also be ameltblown web, a bonded carded web, an air laid web, or a laminate orcomposite including one or more nonwoven webs. The nonwoven web may alsobe formed or modified using a hydraulic entangling process. In oneembodiment, the nonwoven web or composite including it, is neckable, asdefined above. FIG. 4 illustrates a top view of a necked nonwovenmaterial 20, which can be the nonwoven web 10 stretched in the machinedirection 16 prior to lamination to the film 100, to cause elongation ofthe web in the machine direction 16 and narrowing, or neck-in, in thecross direction 18. As shown in FIG. 4, necking causes the individualfilaments 12 to become more aligned with each other, and closer to eachother. When a neckable nonwoven web or composite is employed, it shouldhave a percent neck-down of at least about 15%, more preferably about25-75%, most preferably about 35-65%. Prior to necking, the nonwoven web10 should have a basis weight of about 0.05-4.0 ounces per square yard.(“osy”), preferably about 0.3-2.0 osy, more preferably about 0.4-1.0osy.

When a neckable nonwoven web is used, the nonwoven web can beconstructed from either a variety of polymers. Examples of suitablenon-extendible and less extendible polymers include, without limitation,certain polyolefins, polyamides, and polyesters. Preferred polymers(whether extendible or not) include polyolefins, such as polypropyleneand/or polyethylene. Other suitable polymers include linear low densitypolyethylene copolymers, and copolymers of propylene with up to about10% by weight of a C₂ or C₄-C₁₂ alpha-olefin comonomer.

In another embodiment, the nonwoven web 10 is made of an extendiblepolymer composition, and need not be necked prior to lamination with thefilm 100. Suitable polymers include, without limitation, any of theextendible polymers and blends listed above for the film-formingcomposition. The extendible fibers 12 may be composed of a blend orother combination of an extendible and non-extendible polymer, so longas the extendible polymer is present in sufficient quantity to renderthe nonwoven web extendible in the cross-direction.

In a third embodiment, the cross direction extendible nonwoven web 10 ismade of fibers 12 that are crimped. A wide variety of crimping processesare known in the art. Crimped fibers have accordion-like or spring-likeundulations or microundulations so that when the fibers are extended,they straighten out and/or the undulations are reduced in amplitude.When crimped fibers are used, the polymer of construction need not beextendible, i.e., may be extendible or not extendible.

In yet another embodiment, the nonwoven is formed so that the fibershave very high machine direction (MD) and very little cross direction(CD) orientation. The fibers are then bonded so as to minimize CDbonding of the fibers. This allows the material to extended in the CD.An example of such a material is a bonded carded web (BCW) nonwoven thathas high CD extendibility and low MD extendibility. Other nonwovens,such as spunbonds, can be made to perform like BCW's by forming thespunbond fibers so that the fibers are highly oriented in the MD andbond the filaments with a bond pattern so that the material can readilyextend in the CD. Such a bond pattern would have lower percent bond area(less than 25%) with the bonds lined up predominately in the MD. Thusthere are columns of fibers in the MD which are not bonded adjacent tocolumns of fibers in the MD that are. The unbonded fibers allow thenonwoven to readily extend in the CD while the bonded fibers give thematerial strength and abrasion resistance. BCW materials are describedfurther in Encyclopedia of Polymer Science and Engineering, Vol. 10,Pages 211-212, Wiley & Sons (1987), which is incorporated by reference.

Any nonwoven web is suitable so long as it accommodates thecross-directional stretching of the film in the laminate. A neckednonwoven web accomplishes this by returning toward its original,pre-necked state during cross-directional stretching of the laminate. Aweb made of extendible polymer simply stretches in the cross-directionwith the film. A web of crimped fibers extends in the cross-direction bystraightening out the fibers. A web with high machine directionorientation can extend in the cross-direction by increasing the spacingbetween unbonded portions of adjacent fibers.

The nonwoven web should be selected so as not to substantially impair orlower the WVTR contributed by the film. The bonding technique betweenthe film and web should also be selected so that not more than about15-25% of the interface between the film and web is covered withadhesive or thermally bonded regions, so as not to substantially impairthe WVTR. Before the 25% cross-directional stretch, the laminate mayhave a first WVTR of at least about 500 grams/m²-24 hours, suitably atleast about 1000 grams/m²-24 hours, desirably at least about 1500grams/m²-24 hours. After the 25% cross-directional stretch, the laminatemay have a second WVTR which is at least 225% of the first WVTR,suitably at least 250% of the first WVTR, desirably at least 300% of thefirst WVTR, with the second WVTR not being less than about 4000grams/m²-24 hours. Suitably, the second WVTR maybe at least about 5500grams/m²-24 hours, desirably at least about 7000 grams/m²-24 hours.

FIG. 5 illustrates an integrated process for forming a multilayerbreathable film and a laminate. Referring to FIG. 5, film 100 is formedfrom a film coextrusion apparatus 40 such as a cast or blown unit whichcould be in-line or off-line. Typically the apparatus 40 will includetwo or three extruders 41. To make the core layer, filled resinincluding the polymer matrix material and filler is prepared in a mixer(not shown) and directed to an extruder 41. To make each skin layer,similar additional mixing apparatus (not shown) and extrusion apparatus41 can be used to mix the incompatible polymer components and extrudethem as skin layers on one or both sides of the core layers. Themultilayer film 100 is extruded onto a chill roller 42, which cools thefilm 100. A vacuum box 43 adjacent the chill roller creates a vacuum onthe surface of the chill roller to help maintain the film close to thesurface of the chill roller. Air knives or electrostatic pinners 44 alsourge the film 100 against the roller surface.

From the film extrusion apparatus 40 or off-line rolls supplied, themultilayer film 100 is directed to a film stretching unit 47 which canbe a machine direction oriented, commercially available from vendorsincluding the Marshall and Williams Co. of Providence, R.I. Apparatus 47has a plurality of stretching rollers 46 a-e, which progressivelystretch and thin the film in the machine direction, which is thedirection of travel of the film. The rollers 46 a-e, which are heated tothe desired stretching temperature, apply an amount of stress andprogressively stretch the multilayer film 100 to a stretched lengthwhere the core layer 112 becomes microporous and breathable, and theskin layers 122 and 124 become sufficiently thin, and perhapsmicroporous, so as not to inhibit overall film breathability. While theapparatus 47 is shown with five stretching rollers 46 a-e, the number ofrollers may be greater or less depending on the level of stretch desiredand the amount of stretching between each pair of rollers.

Advantageously, the film 100 may be uniaxially stretched prior tolamination to about 1.1-7.0 times its original length, particularlyabout 1.5-6 times its original length, suitably about 2.5-5 times itsoriginal length, using an elevated stretch temperature as explainedabove. The elevated stretch temperature can be sustained by heating someor all of the stretch rollers 46 a-e. The optimum stretch temperaturevaries with the core layer and skin layer polymers of film 100, and isgenerally below the melting temperature of the matrix polymer in thecore layer 112.

The film 100 may be laminated to the nonwoven web, or webs, usingconventional adhesive bonding or thermal bonding techniques known in theart. Referring again to FIG. 5, film 100 may be laminated to nonwovenweb 20 immediately after the film is stretched. In one embodiment, aneckable nonwoven web 20, which can be a spunbond web, is unwound from asupply roll 62. The neckable material 20 then passes through the nip 64of S-roll arrangement 66, formed by a stack of rollers 68-70, in areverse S-wrap path as shown by the arrows. Rollers 68 and 70 turn at afaster circumferential speed than upstream supply roller 62, causingtensioning and neck-in of web 20. The tensioned, necked material can bepassed under spray equipment 72 (e.g., a meltblown die) which spraysadhesive 73 through die head 74 onto a surface of web 20. With orwithout the adhesive treatment, the necked web 20 can then be joined tomultilayer film 100 and bonded between calender rollers 58, which can beheated if necessary. The rollers 58 can be smooth, patterned, or one ofeach. The rollers 58 can be of steel, rubber, or another suitablematerial. The film 100 in FIG. 5 is simultaneously bonded on its otherside to a second material 30 originating from supply roll 63. The secondextendible material 30 may be a second nonwoven web, or another filmlayer. The resulting laminate 32 is wound and stored on a supply roll60. In addition to the described bonding technique, other bondingtechniques (e.g., other thermal, adhesive or ultrasonic bonding) may beemployed.

After the film and nonwoven web are combined, the resulting laminate canbe easily stretched in the cross-direction to cause greatly improvedbreathability. Alternatively, the laminate may be selectively stretchedin the cross-direction in certain regions of the laminate, to causeimproved breathability only in those regions. Often, the easycross-directional stretch will occur after the laminates have beenconverted into garments, and the garments are put into use. Thecross-directional stretching, which can typically be accomplished atroom temperature by hand, may be on the order of 25% or more (resultingin an increase in the width of the laminate, or selected regions of thelaminate, of 25% or more). This permits the manufactured garments to besomewhat undersized, resulting in a material savings. The effective sizeof the garments can then be increased during donning, when the garmentis stretched or selectively stretched to conform to the contours of awearer.

The cross-direction extendible, breathable laminate may be used in avariety of pant-like absorbent garments, including without limitationdiapers, training pants, swimwear, absorbent underpants, adultincontinence products, feminine hygiene products, and the like. Whenthese garments are installed, the cross-directional stretching of thebreathable laminate (which may be used as a backsheet) occurs primarilyin and below the front and/or back waist regions, causing these regionsto have significantly enhanced WVTR. The crotch region is not stretched,or is stretched a lesser extent, and remains less breathable. Thecross-direction extendible, breathable laminate can also be used inprotective garments, including medical garments and industrialprotective garments. Medical garments include surgical garments, gowns,aprons, face masks, absorbent drapes, and the like. Industrialprotective garments include protective uniforms, workwear, and the like.

Test Procedures

1. WVTR

Test Procedure

A suitable technique for determining the WVTR (water vapor transmissionrate) value of a film or laminate material of the invention is the testprocedure standardized by INDA (Association of the Nonwoven FabricsIndustry), number IST-70.4-99, entitled “STANDARD TEST METHOD FOR WATERVAPOR TRANSMISSION RATE THROUGH NONWOVEN AND PLASTIC FILM USING A GUARDFILM AND VAPOR PRESSURE SENSOR” which is incorporated by referenceherein. The INDA procedure provides for the determination of WVTR, thepermeance of the film to water vapor and, for homogeneous materials,water vapor permeability coefficient.

The INDA test method is well known and will not be set forth in detailherein. However, the test procedure is summarized as follows. A drychamber is separated from a wet chamber of known temperature andhumidity by a permanent guard film and the sample material to be tested.The purpose of the guard film is to define a definite air gap and toquiet or still the air in the air gap while the air gap ischaracterized. The dry chamber, guard film, and the wet chamber make upa diffusion cell in which the test film is sealed. The sample holder isknown as the Permatran-W Model 100K manufactured by Mocon/ModernControls, Inc., Minneapolis, Minn. A first test is made of the WVTR ofthe guard film and the air gap between an evaporator assembly thatgenerates 100% relative humidity. Water vapor diffuses through the airgap and the guard film and then mixes with a dry gas flow which isproportional to water vapor concentration. The electrical signal isrouted to a computer for processing. The computer calculates thetransmission rate of the air gap and the guard film and stores the valuefor further use.

The transmission rate of the guard film and air gap is stored in thecomputer as CalC. The sample material is then sealed in the test cell.Again, water vapor diffuses through the air gap to the guard film andthe test material and then mixes with a dry gas flow that sweeps thetest material. Also, again, this mixture is carried to the vapor sensor.The computer than calculates the transmission rate of the combination ofthe air gap, the guard film, and the test material. This information isthen used to calculate the transmission rate at which moisture istransmitted through the test material according to the equation:

TR ⁻¹ _(test material) =TR ⁻¹ _(test material, guardfilm, airgap) −TR ⁻¹_(guardfilm, airgap)

Calculations:

WVTR: The calculation of the WVTR uses the formula:

WVTR=Fp _(sat)(T)RH/Ap _(sat)(T)(1−RH))

where:

F=The flow of water vapor in cc/min.,

p_(sat)(T)=The density of water in saturated air at temperature T,

RH=The relative humidity at specified locations in the cell,

A=The cross sectional area of the cell, and,

p_(sat)(T)=The saturation vapor pressure of water vapor at temperatureT.

2. Hydrohead Resistance

The hydrohead resistance is a measure of liquid pressure resistance,which is the ability of a film or laminate to withstand application of aload of liquid without fracturing, bursting or tearing. The liquidpressure resistance of a film depends on its thickness, materialcomposition, how it is made and processed, the surrounding environmentand method of testing. Hydrohead values reported herein are measuredaccording to the Hydrostatic Pressure Test described in Method 5514 ofFederal Test Methods Standard No. 191A, which is equivalent to AATCCTest Method 127-89 and INDA Test Method 80.4-92, and which isincorporated herein by reference.

Some of the test results below are for “supported” test specimens. Forthese specimens, the test material was supported by a nylon net (T-246)purchased from Walmart. The netting was approximately 0.1 mm thick andwas made up of nylon threads in hexagonal shapes in the form of ahoneycomb. Each hexagonal shape was approximately 4 mm across.

EXAMPLES Examples 1-3

Samples of three different films were prepared on a cast extrusion lineand stretch oriented in the machine direction to about 4.0 times theiroriginal length. Prior to stretching, each film had a thickness of1.8-1.9 mils. The stretching temperature was about 190° C. for eachfilm. The stretched films were annealed at 210° C. The films had thefollowing compositions.

Example 1 Control

The film of Example 1 was a three-layer A-B-A cast film sold as HuntsmanType 1885, available from Huntsman Packaging Corp., 199 Edison Drive,Washington, Ga. 30763. The film had a core layer containing 42% byweight (69% by volume) Ziegler-Natta catalyzed linear low densitypolyethylene. The polyethylene had an octene comonomer, and a density of0.918 grams/cm³. The core layer also contained 58% by weight (31% byvolume) of stearic acid-coated calcium carbonate particles having a meandiameter of about 1 micron and a top cut of 7 microns. The film had twoskin layers, each containing a mixture of 50.4% by weight ethylene vinylacetate (28% by weight vinyl acetate content), 45.1% by weight of aheterophasic combination of propylene-ethylene copolymers commerciallyknown as Montell KS-357P catalloy, 4% by weight SUPER FLOSS diatomaceousearth made by McCullough and Benton, and 0.5% by weight B-900antioxidant made by Ciba Specialties Company. The skin layersconstituted about 3% of the total film thickness.

Example 2

The film of Example 2 was a single-layer film containing 48% by weight(74.2% by volume) of a polymer combination and 52% by weight (25.8% byvolume) of the same calcium carbonate used in Example 1. The polymercombination contained 41.7% by weight Dow EG-8200, single-site catalyzedvery low density polyethylene having a density of 0.87 grams/cm³ and anoctene comonomer, available from Dow Chemical Co. The polymercombination also contained 58.3% by weight Dowlex 2517, a Ziegler-Nattacatalyzed linear low density polyethylene having a density of 0.917grams/cm³ and an octene comonomer, available from Dow Chemical Co.

Example 3

The film of Example 3 was a single-layer film containing 48% by weight(74% by volume) of a polymer combination and 52% by weight (26% byvolume) of the same calcium carbonate used in Example 1. The polymercombination contained 20.3% by weight Dow EG-8200 and 79.7% by weightDowlex 2517.

For the experiments set forth below, the test film and laminate sampleswere prepared as follows. Adhesive is applied to one face of a Moconmetal sample holder. The sample holder holds six specimens. The adhesivewas applied using a 3M adhesive transfer tape but double-faced stickytape or equivalent would also be acceptable. A piece of the testmaterial put in a mechanical stretcher. The mechanical stretcher hastwelve-inch long jaws that were separated by 20.3 cm (8 inches). Thepiece of test material was put into the mechanical stretcher andelongated 25%, i.e., the jaw separation was increased from 20.3 cm (8inches) to 25.4 cm (10 inches). The sample holder was pressed againstthe test material to adhesively attach the stretched material to thesample holder. The material piece was cut appropriately to allow for thesample holder to be put into the Mocon unit. It is very important toensure that the adhesive being used is strong enough to stop the samplefrom separating from the sample holder and retracting.

In a first set of experiments, the film of Examples 2 and 3 were a)tested for WVTR and hydrohead resistance, then b) stretched by 25% inthe cross-direction at room temperature, then c) tested again for WVTRand hydrohead resistance. Table 1 gives the results.

TABLE 1 Evaluation of Film Samples Hydrohead, mbar WVTR, grams/m²-24hours Before CD Stretch After CD Stretch Example No. Before CD StretchAfter CD Stretch Supported Unsupported Supported Unsupported 2 50012,000 166 42 159 51 3 17,000 64,000 165 68 165 65

As shown above, the minimal cross-directional stretch greatly improvedthe WVTR, and had little effect on hydrohead resistance.

In a second set of experiments, the films of Examples 1-3 wereadhesively laminated to a 33% necked polypropylene spunbond web using 3grams/square meter of Ato Findley 2525A meltblown adhesive. Thelaminates were a) tested for WVTR, then b) stretched at room temperatureby 25% in the cross-direction, then c) tested again for WVTR. Table 2gives the results.

TABLE 2 Evaluation of Laminate Samples WVTR, grams/m²-24 Hours ExampleNo. Before CD Stretch After CD Stretch 1 16,000 32,000 2 800 7,000 319,000 37,000

As shown above, the laminate made from the film of Example 2 gave thebest combination of low WVTR before cross-directional stretching, andmuch higher WVTR after cross-directional stretching.

Examples 4-7

The following Examples further illustrate the performance of variousfilms of the invention, and of film/nonwoven laminates containing thefilms. Each film was prepared on a pilot cast extrusion line, and had aninitial width (prior to stretching) of about 20 inches and an initialthickness of 1.8-1.9 mils. Each cast film was stretch oriented to aboutfive times its original length in the machine direction (MD), using astretching temperature of about 155° C. The stretched films wereannealed at 210° C. Some of the MD stretched films were laminated to apolypropylene spunbond web having a basis weight of about 14 grams persquare meter (gsm), and a fiber denier of 2.0-2.5 dpf. The laminationwas accomplished by using a meltblowing applicator to deposit 2-5 gsm ofFindley 2525A hot melt adhesive to the spunbond web, and then lightlypassing the film and spunbond web together between a pair of niprollers.

MD-stretched films, and laminates including the MD-stretched films, wereextended in the cross direction (CD) by about 25%, to about 125% oftheir width prior to CD stretching, using the method described inExample 3. The force required to extend the films and laminates in thecross direction was measured according to ASTM Procedure D-5035,modified in that a 3-inch wide sample was used instead of a 2-inch widesample, and strain was recorded at 25% cross-directional elongation. TheWVTR of the films and laminates were measured before and after the CDstretching.

The films had the following compositions.

Example 4

The film of Example 4 was a single-layer film containing 47.5% by weight(73.4% by volume) of a polymer combination and 52.5% by weight (26.6% byvolume) of the same calcium carbonate used in Example 1. The polymercombination contained 35.8% by weight Dow ENGAGE EG-8200 (single-sitecatalyzed, very low density polyethylene having a density of 0.87 g/cm³and an octene comonomer), 63.8% by weight Dowlex 2517 (Ziegler-Nattacatalyzed linear low density polyethylene having a density of 0.917g/cm³ and an octene comonomer), and 0.4% by weight Ciba B900 antioxidantfrom Ciba-Geigy Co.

Example 5

The film of Example 5 was a three-layer coextruded film containing acore layer and two skin layers. The core layer contained 44% by weight(29.5% by volume) of a polymer combination and 56% by weight (70.5% byvolume) of the same calcium carbonate used in Example 1. The polymercombination contained 34.1% by weight Dow ENGAGE EG-8200 (single-sitecatalyzed, very low density polyethylene having a density of 0.87 g/cm³and an octene comonomer), 65.5% by weight Huntsman 3106 (Ziegler-Nattacatalyzed, linear low density polyethylene having a density of 0.919g/cm³ and an octene comonomer, available from Huntsman Chemical Co.),and 0.4% by weight Ciba 900 antioxidant. The core layer constituted 98%of the total film thickness.

Each skin layer was composed of Exxon-Mobil LQA-006 (Ziegler-Nattacatalyzed, branched low density polyethylene having a density of 0.918grams/cc, available from Exxon-Mobil Chemical Co.). Each skin layerconstituted 1.0% of the total film thickness.

Example 6

The film of Example 6 was a three-layer coextruded film identical to thefilm of Example 5 except that the Huntsman 3106 in the core layer wasreplaced with an equal amount of Dow NG3310 (Ziegler-Natta catalyzed,linear low density polyethylene having a density of 0.917 g/cm³ and anoctene comonomer, available from Dow Chemical Co.). The remainingcomponents, amounts and layer thicknesses were the same as in the filmof Example 5.

Example 7

The film of Example 7 was a three-layer coextruded film having the samecore layer composition as the film of Example 6. The core layerconstituted 97% of the total film thickness.

Each skin layer contained 50.4% by weight Montell KS357P catalloy (aheterophasic polymer containing i) 50% propylene-ethylene randomcopolymer containing 4% ethylene and 96% propylene, all by weight, ii)5% ethylene-propylene copolymer containing 60% ethylene, essentially inblocks, and 40% propylene, and iii) 45% propylene-ethylene randomcopolymer containing 20% ethylene and 80% propylene), 22.5% by weightExxon-Mobil LD755.12 (ethylene vinyl acetate having a density of 0.951g/cc and containing 28% vinyl acetate), 22.5% by weight Exxon-MobilLD761 (ethylene vinyl acetate having a density of 0.950 g/cc andcontaining 28% vinyl acetate), 4% by weight diatomaceous earth, and 0.6%by weight Ciba 900 antioxidant. Each skin layer constituted 1.5% of thetotal film thickness.

Tables 3 and 4 indicate the breathability before and after the 25% CDstretching, and the stretching force required, for the films andlaminates of Examples 4-7. Table 3 provides the evaluation results forthe films, while Table 4 provides the evaluation results for thelaminates.

TABLE 3 Evaluation of Film Samples WVTR, grams/m²-24 hours BeforeExample No. CD Stretch After CD Stretch Stretching Force, grams 4 8,000Not Available 325-350 5 14,000 40,200 325-350 6 11,000 24,800 325-350 711,000 33,900 325-350

TABLE 4 Evaluation of Laminate Samples WVTR, grams/m²-24 hours BeforeAfter Example No. CD Stretch CD Stretch Stretching Force, grams* 4 NotAvailable Not Available 325-350 5 12,040 27,993 325-350 6 8,618 22,911325-350 7 7,844 22,260 325-350 *estimated based on the stretching forceof the films, which essentially controls the stretching force of thelaminates at low levels of cross-directional extension.

As shown above, the films and laminates of Examples 4-7 had lowcross-directional stretching force as could be easily applied by a userduring installation of a garment containing the films and/or laminates.The CD-stretched films and laminates also had excellent breathability towater vapor, and excellent improvement in breathability compared to theunstretched films and laminates.

While the embodiments of the invention disclosed herein are presentlyconsidered preferred, various modifications and improvements can be madewithout departing from the spirit and scope of the invention. The scopeof the invention is indicated by the appended claims, and all changesthat fall within the meaning and range of equivalents are intended to beembraced therein.

We claim:
 1. A substantially liquid-impermeable film that is extendiblein a cross-direction to a stretched width that is at least 25% greaterthan an unstretched width upon application of a stretching force; thefilm comprising at least one layer which includes a single-sitecatalyzed olefin polymer, a Ziegler-Natta catalyzed olefin polymer, anda particulate filler; the film having a first water vapor transmissionrate of at least about 500 grams/m²-24 hours at the unstretched width;the film having a second water vapor transmission rate which is at least225% of the first water vapor transmission rate and not less than about4000 grams/m²-24 hours, at a stretched width that is 25% greater thanthe unstretched width.
 2. The film of claim 1, wherein the second watervapor transmission rate is at least 250% of the first water vaportransmission rate.
 3. The film of claim 1, wherein the second watervapor transmission rate is at least 300% of the first water vaportransmission rate.
 4. The film of claim 1, wherein the second watervapor transmission rate is at least about 5500 grams/m²-24 hours.
 5. Thefilm of claim 1, wherein the second water vapor transmission rate is atleast about 7000 grams/m²-24 hours.
 6. The film of claim 1, having astretched length in a machine direction that is 1.1-7.0 times anoriginal, unstretched length, wherein the first water vapor transmissionrate exists at the stretched length.
 7. The film of claim 6, wherein thestretched length is 1.5-6.0 times the unstretched length.
 8. The film ofclaim 6, wherein the stretched length is 2.5-5.0 times the unstretchedlength.
 9. The film of claim 1, further comprising at least one skinlayer.
 10. The film of claim 1, wherein the layer includes about 10-55%by volume of the filler and about 45-90% by volume of total polymer, thetotal polymer including about 10-90% by weight of the single-sitecatalyzed olefin polymer and about 10-90% by weight of the Ziegler-Nattacatalyzed olefin polymer.
 11. The film of claim 10, wherein the layerincludes about 15-45% by volume of the filler and about 55-85% by volumeof total polymer.
 12. The film of claim 10, wherein the layer includesabout 25-40% by volume particulate filler and about 60-75% by volume oftotal polymers.
 13. The film of claim 10, wherein the total polymerincludes about 25-75% by weight of the single-site catalyzed olefinpolymer and about 25-75% by weight of the Ziegler-Natta catalyzed olefinpolymer.
 14. The film of claim 10, wherein the total polymer includesabout 30-60% by weight of the single-site catalyzed olefin polymer andabout 40-70% by weight of the Ziegler-Natta catalyzed olefin polymer.15. The film of claim 1, wherein the single-site catalyzed olefinpolymer has a lower density and the Ziegler-Natta catalyzed olefinpolymer has a higher density.
 16. The film of claim 1, wherein thesingle-site catalyzed olefin polymer has a density of 0.870 grams/cm³ toless than 0.900 grams/cm³ and the Ziegler-Natta catalyzed olefin polymerhas a density of about 0.900-0.935 grams/cm³.
 17. A substantiallyliquid-impermeable breathable film that is extendible in a crossdirection to a stretched width that is at least 25% greater than anunstretched width upon application of a stretching force; the filmcomprising a filled layer which includes about 10-55% by volume of aparticulate filler and about 45-90% by volume of total polymer; thetotal polymer including about 10-50% by weight of a single-sitecatalyzed very low density polyethylene and about 50-90% by weight of aZiegler-Natta catalyzed linear low density polyethylene; the film havinga first water vapor transmission rate of at least about 500 grams/m²-24hours at the unstretched width and a second water vapor transmissionrate which is at least about 4000 grams/m²-24 hours at a stretched widththat is 25% greater than the unstretched width.
 18. The film of claim17, wherein the filled layer comprises about 15-45% by volume of thefiller and about 55-85% by volume of the total polymer.
 19. The film ofclaim 17, wherein the filled layer comprises about 25-40% by volume ofthe filler and about 60-75% by volume of the total polymer.
 20. The filmof claim 17, wherein the total polymer comprises about 25-50% by weightof the very low density polyethylene and about 50-75% by weight of thelinear low density polyethylene.
 21. The film of claim 17, furthercomprising at least one skin layer.
 22. The film of claim 17, whereinthe second water vapor transmission rate is at least 225% of the firstwater vapor transmission rate.
 23. A substantially liquid-impermeablefilm that is extendible in a cross direction to a stretched width thatis at least 25% greater than an unstretched width upon application of astretching force; the film comprising a filled layer which includes alower density olefin polymer having a density of 0.870 grams/cm³ to lessthan 0.900 grams/cm³, a higher density olefin polymer having a densityof 0.900-0.935 grams/cm³, and a particulate filler; the film having afirst water vapor transmission rate of at least 500 grams/m²-24 hours atthe unstretched width and a second water vapor transmission rate atleast 225% of the first water vapor transmission rate and at least 4000grams/m²-24 hours at the stretched width.
 24. The film of claim 23,wherein the lower density olefin polymer comprises a single-sitecatalyzed polymer.
 25. The film of claim 24, wherein the higher densityolefin polymer comprises a Ziegler-Natta catalyzed olefin polymer. 26.The film of claim 23, wherein the second water vapor transmission rateis at least 250% of the first water vapor transmission rate.
 27. Thefilm of claim 23, wherein the second water vapor transmission rate is atleast 300% of the first water vapor transmission rate.
 28. The film ofclaim 23, wherein the filled layer comprises about 10-55% by volume ofthe filler and about 45-90% by volume of total polymer, the totalpolymer including the lower density olefin polymer and the higherdensity olefin polymer.
 29. The film of claim 28, wherein the totalpolymer includes about 25-75% by weight of the lower density olefinpolymer and about 25-75% by weight of the higher density olefin polymer.30. The film of claim 28, wherein the total polymer includes about30-60% by weight of the lower density olefin polymer and about 40-70% byweight of the higher density olefin polymer.